Insulating and cooling means for transformers



A. LINDSTBO'M. INSULATING AND COOLING MEANS FOR TRANSFORMERS.

AiPLlCATION FILED MAR-6,1919.

Patented Mar. 16, 1920.

BAN

ARVID LINDSTRM, 0F WSTEIBS, SWEDEN.

INSULATING AND COOLING MEANS FOR TRANSFORMERS.

Specification of Letters Patent.

`Application led March 6, 1919. Serial No. 281,088.

To aZZ wlw/lt 'it may concern:

Be it known that I, ARVIDv LINDsTRM, subject of the King of Sweden, residing at Almelund 3, VVasteras, Sweden, have in-l vented Acertain new and useful Improvements in Insulating and Cooling Means for Transformers, of which the following is a specification.

It is known that the dielectric strength of gases increases with the pressure of the gas. For air, carbonio acid, nitrogen and others it has been found, that exact, or nearly exact proportionality prevails between the strength (break-down voltage) and the pressure within wide limits. It has therefore been proposed to employ compressed gas as insulating medium in transformers instead of oil or air of atn'xospheric pressure. As far as known, it has only come to suggestions in'this direction, probably depending upon the fact that gases, at atmospheric pressureas well as in a compressed state, are bad conductors of heat, nor are they able to carry off the heat by so-called convection in such degree as for instance oil. The employment Iof the latter in transformers is based not only upon its insulating but also,

and not least, upon its heat-conducting properties. If a compressed gas were employed instead of oil under equal conditions in other respects, the temperature of the active parts of the transformer (winding and core) would be correpondingly higher.

The object of the present invention is to provide a transformer having a compressed gas as insulating and cooling medium, in

which a considerable difference of temperature can be allowed between the actlve parts and the cooling medium, without surpassing the allowable absolute temperature .of the former parts. Thisv is ,accomplished by keeping the compressed gas and the inside of the casing at so low temperature, that the winding, in spite of a high difference of temperature with respect to the gas, can be moderately warm or even cold.

In the accompanying drawings, I have shown means for carrylng out my invention,

which have been found to be very eient for the purpose.` l

Figure 1 is a side elevation, partly in section, ofwone form, and

Fig. 2 is a similar view of a slightly different form.

In Fig. l a. is the inlet to the coil c.

is a high pressure compressor from which leads the piped to the coil b. e is a pipe from the coil Z) to the expansion nozzles f' and g. This pipe e is provided with a valve L.. z' z' are terminals for suitable connections on the casing j. is is the low tension winding, and Z the high tension winding. m is insulation. n is the low pressure pipe connecting the compressor c with the casing y'. In Fig. 2 the casing j contains the tubular cooling coil 0.

' For cooling the gas many different ways may be employed, only a couple of which may be mentioned here.

(l) The gas is compressed with removal of heat to a high pressure and rather low temperature (which may be so low that the gas is liquefied). From this state, the gas is allowed to expand in entering the transformer casing to the pressure prevailing therein which is from five to ten atmospheres so that the temperature of the gas is considerably lowered duringA the expansion. As the gas is heated by absorbingythe loss heat of the transformer, it is removed therefrom` to be compressed and cooled Patented Mar. 16, 1920.

again, andso on. The gas thus is brought to circulate continuously with a speed depending upon the load gf the transformer and on the temperature allowed for its winding and other parts. l

(2) The gas is permanently inclosed within the transformer under a certain pressure which may be maintained by means of a compressor or the like. The gas and the inside of the casing are cooled by means of pipes traversed by a cooling medium, gaseous or liquid in about the same manner as that employed in ordinary cooling plants.

If in any of these or in another manner the temperature of the gas is kept very low, a further increase of the dielectric strength of the gas is gained, as the latter is shown by experience to be substantially inversely proportional to its a'bsolute temperature. 'If the gas and the interior of the casing are kept at so low temperature that the temperature of the winding also will be quite or comparatively low the advantage is gained that the specific-resistance of the winding will be correspondingly low and thus either the ohmic losses or the necessary Awinding area' and copper quantity On the other hand, such a 10W temperature is unsuitable for the iron core of the `trans-` former, as the eddy current' losses therein will be the greater, the lower the resistivity and the temperature of the iron are. It is therefore preferred to provide a heat insulation for the iron core so as to make its temperature higher than that of the Winding. By a special arrangement it can be put in direct heat conducting communication With the surrounding air so as to yield a greater or smaller portion of its heat directly thereto, so that the said portion Will not contribute to the heating of the compressed gas and the Winding.

Having now described my invention and the manner of its operation, l declare that what l claim is:

l. ln transformers,.the colnlbination of a casing filled with an insulating gas at a pressure superior to the atmospheric one, a compressor for maintaining said pressure and a device for producing low temperature in the transformer casing by gas expansion.

Q. ln transformers, the combination of a casing capable of sustaining a pressure superior to the atmospheric one, a compressor for compressinga gas to a very high pressure, a cooling device for said compressed gas, and an expansion device between'the 30 cooling device and the transformer casing. In transformers, the com'bination of an iron core, a winding, a casing inclosing both, means for circulating a gas at a high pressure and low temperature through said casing and around said Winding, and an insulating layer surrounding said iron core so as to protect it against the cooling action of said Gas.

4. lzn transformers, the comIb-inationlof an iron core, a winding, a casing inclosing both and in heat-conducting contact With said iron core, means for circulating a gas at high pressure and 10W temperature through said casing and around said Winding, and an insulating layer surrounding said iron core on the sides not in contact With the casing v In testimony whereof l have aiiiXed my signature in the presence of 'two Witnesses.

Anvin LiNDsTRoi/r.

Witnesses BIRGER NORDFELDT,

BENQ BLssoN. 

